[SkyMarshal]

Games, document formats, workforce familiarity, and pre-existing infrastructure (Exchange, bureaucratic corporate IT depts, etc).

Still a fairly large hurdle to overcome, but I'm hoping Valve can at least break down the games one.

[gizmo686]

Document formats don't seem to be a problem any more. Back when MS switched to .docx people I knew continued using .doc to maintain compatibilty with old versions. I actually got support for the 2007 formats before most of my windows using friends. As long as you change your default file format to the MS one, I don't think you'll run into issues on that front.